With the advent of OPEC, and the high cost and short supply of hydrocarbons, alternatives for existing vapor degreasing solvents has intensified.
The ordinary vapor degreasing solvents are normally chlorinated hydrocarbon ones, which meet the criteria of having no flash point and possessing good contaminant solvency and reusability through reclamation processes.
The prior art has utilized, as the basic vapor degreasing solvent, perchlorethylene for use in the ubiquitous vapor degreasing machine and operation. The perchlorethylene ordinarily is used in conjunction with a stabilizer which will extend the useful life of the vapor degreasing solvent.
That is, in the vapor degreasing process, a non-flammable solvent is boiled to produce a vapor zone, the height of which is controlled by condensing coils. Cold work is introduced into the vapor, causes vapor condensation thereon, and the contaminant carried on the cold work, usually oil, grease or flux, is flushed off by the liquid solvent condensate. The contaminant, along with the condensate, is returned to the boiling sump of the vapor degreasing machine. This condensate, or distillate, then is revaporized to repeat the cycle of cleansing through condensation.
The work piece which is to be cleansed is held in the vapor zone until the temperature thereof reaches the vapor temperature within the vapor zone, at which time condensation stops. Vapor flushing is usually followed by pure distillate spray and/or liquid immersion. The cool, pure distillate reduces the temperature of the metal surface below the vapor temperature producing a second vapor condensation. When the work piece again reaches vapor temperature, it is withdrawn from the vapor zone, clean and dry.
The vapor degreasing solvent is used at its boiling point in order to produce the vapor zone necessary for vapor condensation and resultant cleaning.
Where perchlorethylene alone or in conjunction with certain stabilizers to prolong the life thereof are utilized, serious drawbacks occur.
That is, during the degreasing operations, the perchlorethylene is adversely affected by the increasing amounts of contaminants finding their way into the boiling sump in that the boiling temperature of the perchlorethylene in the sump increases as the amount of contaminant increases. To compensate for this added contamination, solvent manufacturers add acid inhibitors or stabilizers in an effort to extend its vapor degreasing life.
When the temperature in the boiling sump of the vapor degreasing device reaches and exceeds the range of approximately 256.degree.-258.degree. F., normally signifying 25-30% volume percent contamination, depletion of the stabilizers is nearly complete and additional usage of the perchlorethylene is not recommended because of acidic breakdown and failure.
Vapor degreasing handbooks recommend that perchlorethylene vapor degreasers be shut down and the degreasing operation terminated to allow clean-out of the boiling sump once the boiling sump temperatures reach about 256.degree. F. The general criteria, measured in other terms for solvent rejuvenation, are when the boil sump specific gravity is 1.44 or has an acid acceptance value of about 0.02-0.06, or wherein the pH value is between about 5.5-6.0.
In order to extend the life of perchlorethylene by as much as 50%, and to reduce the boiling sump temperature, even with contamination present, and to provide a satisfactory vapor degreasing solvent of lower cost, it has been found that the addition of trichlorethylene to perchlorethylene in an amount to reduce the initial boiling temperature of the resultant blend to about 240.degree. F. achieves definite attributes, while alleviating many of the detriments found in prior art uses and methods of vapor degreasing using perchlorethylene alone or with stabilizers to extend its useful life.